When is it appropriate to use AJAX?

Question

When is it appropriate to use AJAX?
what are the pros and cons of using AJAX?

In response to my last question: some people seemed very adamant that I should only

Answer 1

Ajax gives you two big things:

Responsiveness - you can update only parts of a web page at a time if need be (saving the time to re-load a page). It also makes it easier to page data that is presented in a table for instance.

User Experience - This goes along with responsiveness. With AJAX you can add animations, cooler popups and special effects to give your web pages a newer, cleaner and cooler look and feel. If no one thinks this is important then look to the iPhone. User Experience draws people into an application and make them want to use it, one of the key steps in ensuring an application's success.

For a good case study, look at this site. AJAX effects like animating your new Answer when posted, popups to tell you you can't do certain things and hints that new answers have been posted since you started your own answer are all part of drawing people into this site and making it successful.